DOI: 10.1590/0004-282X20160129
CLINICAL SCALES, CRITERIA AND TOOLS
Brazilian-Portuguese translation,
cross-cultural adaptation and validation
of the Myasthenia Gravis Composite scale.
A multicentric study
Tradução,adaptação cultural e validação da escala composta de Miastenia Grave para a
lingua portuguesa do Brasil. Estudo multicêntrico
Ezequiel Fernandes Oliveira1, Valéria Cavalcante Lima2, Eduardo Araujo Perez3, Melissa Nunes Polaro4,
Berenice Cataldo Oliveira Valério4,João R Pereiro5, Sergio Roberto Nacif5, Claudia Santos Oliveira1,
Acary Souza Bulle Oliveira2, Luis Vicente Franco Oliveira1
Myasthenia gravis (MG), a chronic autoimmune disease, is characterized by progressive weakness and fatigue of skel-etal muscle caused, in 85% to 90% of patients, by antibodies
against the acetylcholine receptor (AChR) of the post-synaptic membrane of the neuromuscular junction1.here is also a
smaller number of patients showing autoantibodies against
1Universidade Nove de Julho, Programa de Pós Graduação Mestrado e Doutorado em Ciências da Reabilitação, São Paulo SP, Brasil;
2Universidade Federal de São Paulo, Departamento de Neurologia e Neurocirurgia, Divisão de Doença Neuromuscular, São Paulo SP, Brasil;
3Faculdade de Ciências Médicas da Santa Casa de São Paulo, Programa de Mestrado e Doutorado em Pesquisa em Cirurgia, São Paulo SP, Brasil;
4Faculdade de Ciências Médicas da Santa Casa de São Paulo, Departamento de Clínica Médica, Disciplina de Neurologia, São Paulo SP, Brasil;
5Hospital do Servidor Público Estadual, Programa de Pós Graduação em Ciências da Saúde, São Paulo SP, Brasil.
Correspondence: Luis Vicente Franco Oliveira; Laboratório de Sono da UNINOVE; Rua Vergueiro 235/249; 01504-001 São Paulo SP, Brasil; E-mail: oliveira.lvf@pq.cnpq.br
Conflict of interest: There is no conlict of interest to declare.
Support: LVFO received Research Productivity modality IB grants from Conselho Nacional de Desenvolvimento Cientiico e Tecnologico (CNPq; process no. 313053/2014-6) and, EFO receives grants from Fundaçao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP; protocol no. 2015/11738-6. Received 16 March 2016; Received in inal form 01 June 2016; Accepted 20 June 2016.
ABSTRACT
Objective: To perform the translation, cultural adaptation and validation of the Myasthenia Gravis Composite (MGC) scale in Brazil.
Methods: The study was conducted at three neuromuscular disease research centers in accordance with the international ethical standards, following a multi-modal approach and was conducted in three steps consisting of translation, cultural adaptation, and validation according to international guidelines. The inal version of the MGC was applied in a sample of 27 MG patients and the total score was compared to a Portuguese version of the MG-QOL-15. Results: The internal consistency veriied by Cohen’s Kappa test was excellent (0.766). The correlation between the MGC and MG-QOL-15 was strong (R = 0.777; p = 0.000). No signiicant differences were found between the responses of patients in the irst and second applications of the MGC. Conclusion: The MGC scale, validated into Brazilian Portuguese, has proven to be a reliable instrument that is easy to use, and is highly reproducible.
Keywords: myasthenia gravis; translating; surveys and questionaires.
RESUMO
Objetivo: Realizar a tradução e a adaptação transcultural da escala composta de Miastenia Grave (ECMG) Myasthenia Gravis Composite (MGC) no Brasil. Métodos: O estudo foi realizado em três centros de investigação em doenças neuromusculares, de acordo com as normas éticas internacionais, consistindo em tradução, adaptação cultural e validação de acordo com as diretrizes internacionais. A versão inal do MGC ECMG foi aplicada em vinte e sete pacientes com MG e a pontuação total foi comparada ao questionário MG-QOL 15. Resultados: A consistência interna veriicada pelo teste Kappa de Cohen foi excelente (0,766) e a correlação entre o a ECMG MGC e MG-QOL 15 foi positiva (R = 0,777; p = 0,000). Não foram encontradas diferenças entre as respostas dos pacientes na primeira e segunda aplicação da MGC. Conclusão: A ECMG escala MGC validada para o Português do Brasil provou ser um instrumento coniável, de fácil aplicação e altamente reprodutível.
the muscle-speciic kinase (MuSK) or the low-density lipo -protein-related protein 4 (LRP4) and even against agrin2.
he prevalence of MG varies from 1.7 to 21.3 cases per
million people per year in the general population, mainly
afecting individuals aged 20-40 years, and more women than men (ratio 3:2). he mortality rate varies from 0.06 to 0.89 per
million people each year3,4.
Disease severity depends on the compromised mus-cle groups, varying from mild, with purely ocular symp-toms, to the most serious cases with generalized mus-cle weakness and respiratory failure1. The Myasthenia
Gravis Committee Foundation of America (MGFA) cat-egorizes MG into five levels of severity according to the appearance of symptoms and the anatomical distribu-tion of affected muscle groups5.
Health Related Quality of Life (HRQoL) is an important component in the evaluation of MG patients, as the disease
severity can vary widely. he assessment instruments of HRQoL and clinical progression can be generic or speciic to
a particular group of diseases, such as MG6. Clinical trials to
test new therapeutic interventions require some scale of clin-ical evaluation to assess the level of disease severity and the response to therapy7,8.
Information about clinical evaluation and HRQoL,
obtained through speciic instruments, enable a better
understanding of the patient’s needs, and allow provision of adequate clinical support6. he more speciic the instrument,
the more relevant it becomes for evaluation and monitoring of disease progress.
The HRQoL and clinical status measures, obtained through patient-oriented instruments, are considered essential in the evaluation of neurological diseases, espe-cially in those diseases that may affect a patient’s general status, such as MG. Patient-derived tools have added a new dimension to clinical outcome evaluation. These are important, both for assessing individual patients in the neurology clinic, and for international comparisons, mul-ticenter trials and other types of collaborations9. Previous
studies have described a significant correlation between HRQoL and severity of MG10,11,12.
We found only three specific tools for evaluating HRQoL in MG patients in the international scientific lit-erature (Myasthenia Gravis Questionnaire13, Myasthenia
Gravis-specific Activities of Daily Living Profile14,15,
Questionnaire of Life Quality Specific for Myasthenia
Gravis – 15 items (MG-QOL-15)16) and two instruments
to assess the clinical evaluation of patients with MG
(Quantitative Myasthenia Gravis Score17 and Myasthenia
Gravis Composite scale (MGC)18). From these
instru-ments, only the MG-QOL-15 has been translated into Brazilian Portuguese19. Therefore, it was important to
study the translation, cultural adaptation and validation of the MGC in Brazilian patients.
METHODS
The study was conducted at three neuromuscular dis-ease research centers in accordance with the ethical
stan-dards established in the 1961 Declaration of Helsinki (as revised in Hong Kong in 1989 and Edinburgh, Scotland in
2000) and complied with the Regulatory Guidelines and
Norms for Research Involving Human Subjects of the
National Health Board of the Brazilian Health Ministry issued in December 2012. This study is part of a research
protocol that was approved by the Human Research Ethics
Committee of Nove de Julho University (Brazil) under
pro-cess no. 360.488 and is registered with the World Health
Organization (WHO) under Universal Trial Number (UTN)
U1111-1147-7853 and the Brazilian Registry of Clinical Trials (REBEC) RBR -7ckpdd. A written informed con -sent was obtained, and subjects were allowed to withdraw from the study at any time without consequence.
he study included patients with a clinical diagnosis of MG according to the MGFA, aged 18–75 years, both genders,
who were clinically stable and who agreed to participate by signing the informed consent form. We excluded patients with other neuromuscular disorders, episodes of acute clini-cal decompensation in the two months prior to consider-ation for inclusion, and those with a history of stroke, mental instability, or drug or alcohol abuse.
The Instrument
The MGC scale is a valid and reliable instrument used to evaluate the clinical status of patients with MG both in clinical practice, and in scientific research. The scale was validated through tests conducted in 2008 and 2009
in 11 research centers in the United States of America and Europe20. The MGC is an ordinal scale,
consist-ing of 10 items, each representconsist-ing a function commonly affected by MG. The response categories of MGC items
are weighted. For example, ‘ptosis’ scores 3 points, while
‘severe weakness of hip flexion’ is equivalent to 5 points, and severe respiratory weakness (i.e. ventilator-dependent
patients) equates to 9 points. The maximum MGC score is 50, and directly relates to patient condition i.e., a high
score reflects severe disease. A reduction of 3 points in
the score may indicate a significant and reliable clinical improvement in patients with MG.
Translation, cross-cultural adaptation, and validation
he study design followed a multi-modal approach and
was conducted in three stages consisting of translation, cul-tural adaptation, and validation of the MGC according to international guidelines proposed and developed in other linguistic and socio-cultural contexts21,22,23,24,25. Figure 1
Translation
According to the established protocol previously pub-lished26, two qualiied Brazilian translators, one a professional
scientiic English translator who is unfamiliar with the area of
expertise, the other a bilingual neurologist, performed
inde-pendent Brazilian Portuguese translations. hen, a committee
of four neurologists and two physiotherapists, all bilingual,
compared these two initial translations, creating a new, irst
version of the scale in Brazilian Portuguese. All members of this committee were bilingual university professors and research-ers with clinical experience in neuromuscular diseases and
had advanced knowledge of the English language.
Figure 1. Flow chart of the methodological approach.
Questionnaire in the original version
Committee – Evaluation of translated versions.
First version in Portuguese
Qualified translator Qualified translator
Reverse translation Reverse translation
Myasthenia Gravis Composite Scale Translation into
Brazilian Portuguese.
Translation into Brazilian Portuguese.
Native translator, not healthcare professional.
Native translator, healthcare professional.
Psychometric evaluation: reability and pre-test
Application in 20 patients with confirmed diagnosis of MG.
Psychometric evaluation: validation
Application of final version in 27 patients with MG.
Cross-cultural adaptation
Twnty professionals from clinical neurology and rehabilitation fields.
Expert Committee
Was compared to the original version, analyzed the discrepancies and generated
Reverse-translation
Two native English speakers, a layperson and a professional
translator, subsequently performed two reverse-translations of the preliminary Brazilian Portuguese version of the scale.
hese translators were not informed about the study objec
-tives and had no access to the original version. his
reverse-translation aimed to prove that the new version was equiva-lent to the original.
Another expert committee, comprising one methodolo-gist, six health professionals, two native-speaking profession-als and the translators, compared the two reverse-translation
versions with the original English version of the MGC, made necessary adjustments, and generated the inal version in Portuguese. he second Portuguese version of the scale was
established after consensus was reached among committee members on each item.
Cross-cultural adaptation
he second version of the scale, translated into
Portuguese, underwent a semantic analysis, and was ana-lyzed by twenty health professionals, specializing in clinical neurology and rehabilitation medicine (10 physicians and 10 physiotherapists), to determine whether the terms used
were easy to understand. his step was performed to ensure
that the translated items were equivalent to the original, and included an assessment of the degree of understanding of the issues proposed.
Health professionals involved in this research phase made comments about the understanding of the scale. Any ambig-uous terms were highlighted and discussed by the members of the study committee, and were replaced by other terms with semantic equivalence, appropriate to Brazilian culture, thereby generating a third version in Portuguese, without compromising the original version.
Psychometric evaluation
Reliability
To check inter-rater reliability, the third Portuguese version was administered by 10 health professionals to
20 patients with a conirmed diagnosis of MG (15 women), on two diferent occasions, at the same time of the day, with an interval of 48 hours, to assess test-retest reliability. hese
results were used to determine the level of semantic
under-standing to consolidate the inal version of the MGC scale. he inal version of the MGC scale translated into Brazilian
Portuguese is presented in Figure 2.
Pre-test
The content validity was assessed qualitatively in a pilot study, in which the patients provided critical feedback on the design, content, and structure of the questionnaire, and in consultation with specialized clinicians in the field. The validity of the questions on the clinical characteristics
and disease severity of MG were evaluated retrospectively by the two main investigators. They were blinded to the questionnaire results when registering the symptoms in the medical records of the 20 patients who participated in the pre-test stage.
he self-reported clinical characteristics of the disease
at onset were compared with the symptoms reported in the patient’s medical record, and the clinical symptoms reported in the medical records were considered to be the closest to a gold standard evaluation of the patients’ symptoms.
Validation
Forty patients (29 women) with a conirmed diagno
-sis of MG, and classiied according to MGFA, were invited
to participate in this step of the study. Twenty-seven patients (21 women) accepted, comprising 11 patients from
Setor de Investigação de Doenças Neuromusculares da Universidade Federal de São Paulo (UNIFESP), 11 patients
from Departamento de Neurologia da Faculdade de Ciências
Médicas da Santa Casa de São Paulo (FCMSC), and ive
patients from Departamento de Neurologia do Hospital do
Servidor Público Estadual (HSPE).
Demographic and clinical data were collected, along with details of current MG-related symptoms and thera-peutic strategies. We excluded nine patients due to cogni-tive impairment, illiteracy and/or other chronic diseases and four patients because of a diagnosis of congenital myasthenic syndrome. The final version of the MGC was
administered to in a final sample of 27 MG patients and
the total score was compared to a Portuguese version of the MG-QOL-15, validated in Brazil, and commonly used to assess quality of life in MG19.
he MG-QOL-15 is an efective, quick, and easy-to-use
instrument, consisting of 15 items, graded on a scale of 0-4,
evaluating three dimensions of the HRQoL. he highest pos
-sible score is 60 points, indicating a poor quality of life as perceived by the patient. hese 15 items eiciently evaluate
physical, social, and psychological aspects of life, which are essential components for the interpretation of the HRQoL.
he instrument does not have a speciic cut-of value16,19.
Statistical analysis
Initially, the Shapiro-Wilk test was used to verify the
normal distribution of the sample data. Parametric data were expressed as mean and standard deviation, including anthropometric values, age, and the circumferences of the neck and abdomen. Non-parametric data were expressed by standard error.
In the pre-test, we used Cohen’s Kappa coeicient for ordinal measures. he Kappa statistic is frequently used to
test inter-rater reliability. Rater reliability is important as it
relects the accuracy of the data collected. Measurement of
Pearson’s rank correlation coeicient was used for corre -lation of the subjective assessment of MGC and MG-QOL 15.
A p value < 0.05 was considered signiicant. Statistical anal
-yses were performed with the StatView 5.0 (SAS Institute, Cary, N.C., USA), and SPSS software (version 23.0, SPSS Inc. Chicago, IL, USA).
RESULTS
here were 27 patients (21 women) with a conirmed
diagnosis of MG acquired autoimmune form, and a mean
age of 46.55 ± 11.71 years, range 32–74 years, enrolled in this study. he average duration of illness in these patients was 11.33 ± 8.49 years. According to the classiication of MGFA,
two patients were class I, 17 were class II, eight were class III, and none were in classes IV and V. Ninety-eight percent of
patients were taking cholinesterase inhibitors and 28% were taking an immunosuppressant. Clinical and demographic features of the MG patients are presented in the Table.
Reliability and validity
he average time required for completing the MGC by patients was 32 minutes. he expression “ptosis, ascending naturally”, in the original version, was replaced by “ptosis, look -ing up easily”. Items used in the evaluation of muscle strength
of neck lexion/extension, hip lexion, and shoulder abduction generated the greatest diiculty. Speciically, the grading of muscle weakness as moderate weakness posed problems. he
original version emphasizes that moderate weakness should
Nota: Observe que “fraqueza moderada” para os itens pescoço e membros deve ser interpretada como fraqueza equivalente a 50%±15% do esperado para uma força normal. Qualquer fraqueza mais leve do que isto seria classiicada como leve e qualquer fraqueza mais grave seria classiicada como grave.
Total de pontos: ______________________
Figure 2. Portuguese-Brazil version of Myasthenia Gravis Composite Scale.
Ptose (olhar para cima
facilmente) > 45 segundos 11–45 segundos 1–10 segundos Imediata
(exame médico) 0 1 2 3
Visão dupla (olhar ixo lateral) (esquerda ou direita).
> 45 segundos 11–45 segundos 1–10 segundos Imediata
(exame médico) 0 1 3 4
Fechamento dos olhos Normal Fraqueza leve (abertura
com esforço externo) Fraqueza moderada Fraqueza grave
(exame médico) 0 0
(podem ser abertos facilmente)
(incapaz de manter os olhos fechados)
1 2
Fala Normal Gagueira intermitente ou
fala nasal
Gagueira constante ou fala nasal que pode ser
compreendida
Diiculdade no entendimento da fala
(História do paciente) 0 2 4 6
Mastigação Normal Fadiga com alimentos
sólidos
Fadiga com alimentos
moles Tubo gástrico
(História do paciente) 0 2 4 6
Deglutição Normal
Raros episódios de engasgo ou diiculdade
para engolir = 2
Diiculdade frequente na deglutição com necessidade de alteração
na dieta
Tubo gástrico
(História do paciente) 0 5 6
Respiração Normal Dispneia de esforço Dispneia em repouso Ventilador dependente
(consequência da MG) 0 2 4 9
Flexão ou extensão de
pescoço. Normal Fraqueza leve Fraqueza moderada Fraqueza grave
(exame médico) 0 1 (~50% fraca ± 15%) = 3 4
Abdução de ombros Normal Fraqueza leve Fraqueza moderada Fraqueza grave
(exame médico) 0 2 (~50% fraca ± 15%) = 4 5
Flexão do quadril Normal Fraqueza leve Fraqueza moderada Fraqueza grave
be equal to approximately 50% ± 15% of the expected normal
force. Accordingly, we added a note explaining how to grade
moderate muscle weakness to the inal version of the scale. he internal consistency veriied by Cohen’s Kappa test was excellent (0.766). Patients scored an average of 12.93 ± 6.92 in the MGC scale and an average of 21.38 ± 12.07 in the MG-QOL-15 scale. he correlation between the MGC and MG-QOL-15 was strong (R = 0.777; p = 0.000). No sig
-niicant diferences were found between the responses of patients in the irst and second applications of the MGC.
DISCUSSION
In recent years, disease-speciic, patient-derived question -naires have become important measures to describe disease sever-ity when compared with generic, patient-derived instruments.
According to our knowledge, this is the irst study of the
translation and validation of the MGC scale to a language
other than English. Translation of the MGC to Brazilian Portuguese was successful, and reverse-translation to English corresponded very well with the original version. he MGC
scale was properly translated and culturally adapted
follow-ing a deined sequence of actions in accordance with the
standards for cultural adaptation21,22,23,24,25.
In 2012, a Task Force of the Medical Scientiic Advisory
Board of the MGFA recommended using the MGC as the quantitative measure for determining improvement or dete-rioration in patients with generalized MG27.
he MGC can be used in daily practice and in clinical tri
-als. his instrument difers from most scales in that it is a
hybrid of patient-reported and physician-reported test items. It is not surprising that certain patient-reported test items perform better than their physician-reported examination counterparts, and thus justify inclusion in the MGC.
he validity and reliability of the MGC for measuring dis -ease severity in MG was previously demonstrated using con-ventional psychometric tests28,29.
he evaluation of the HRQoL of a patient can inluence
therapeutic decisions and provide a better understanding of their needs, allowing the adoption of an appropriate thera-peutic strategy16,30. A disease-speciic instrument may be the
most relevant clinical and functional assessment of the
dis-ease state, avoiding inefective approaches28.
In the validation phase, the Brazilian version of the MGC was very well understood and accepted by patients and by health professionals. Neither patients nor professionals
had diiculties completing the questionnaire. In the valida -tion phase of our study, the MGC was compared with the MG-QOL-15, considered the gold standard HRQoL
assess-ment instruassess-ment in MG, with a positive correlation. his
result corroborates other studies that validated the use of the MGC as an evaluation tool in patients with MG16,18.
Factors related to the disease can inluence HRQoL in
MG, such as the predominant symptoms, the frequency of
myasthenic crisis and the therapeutic strategy adopted. he frequency and severity of MG symptoms also inluence the perception of HRQoL. herefore, it is expected that a poor
clinical situation will lead to a poor HRQoL result.
In conclusion, the original version of the MGC scale, having been translated, culturally adapted, and validated into Brazilian Portuguese has proven to be a reliable instrument that is easy to use, highly reproducible, and can be used in both clinical prac-tice and clinical trials in the evaluation of patients with MG.
Table. Clinical and demographic features of the patients with myasthenia gravis.
Variables Patients (n = 27) (%)
Female/male 21/jun -
Age (years) 46.55 ± 11.71
-Disease classiication
Acquired autoimmune 27
-MGFA
I 2 7.4
IIA 15 55.5
IIB 2 7.4
IIIA 4 14.8
IIIB 4 14.8
MGC score 12.8 ± 7
-MG QOL – 15 score 21.7 ± 12.2
-MGFA: Myasthenia Gravis Foundation of America Clinical classiication; MGC: Mysthenia Gravis Composite scale; MG-QOL: Questionnaire of Life Quality Speciic for Myasthenia Gravis – 15 items.
References
1. Drachman DB. Myasthenia gravis. N Engl J Med. 1994;330(25):1797-810.
2. Patrick J, Lindstrom J. Autoimmune response to acetylcholine receptor. Science. 1973;180(4088):871-2. doi:10.1056/NEJM199406233302507
3. Carr AS, Cardwell CR, McCarron PO, McConville J. A systematic review of population based epidemiological studies in Myasthenia Gravis. BMC Neurology. 2010;10(1):46. doi:10.1186/1471-2377-10-46
4. Mao ZF, Mo XA, Qin C, Lai YR, Hartman TCO. Course and prognosis of myasthenia gravis: a systematic review. Eur J Neurol. 2010;17(7):913-21. doi:10.1111/j.1468-1331.2010.03017.x
6. Cella DF, Tulsky DS. Measuring quality of life today: methodological aspects. Oncology (Willinston Park). 1990;4(5):29-38.
7. Tindall RS, Rollins JA, Phillips JT, Greenlee RG, Wells L, Belendiuk G. Preliminary results of a double-blind, randomized, placebo-controlled trial of cyclosporine in myasthenia gravis. N Engl J Med. 1987;316(12):719-24. doi:10.1056/NEJM198703193161205
8. Tindall RS, Phillips JT, Rollins JA, Wells L, Hall K. A clinical therapeutic trial of cyclosporine in myasthenia gravis. Ann N Y Acad Sci. 1993;681 1 Myasthenia GR:539-51. doi:10.1111/j.1749-6632.1993.tb22937.x
9. Tonali P, Padua L, Sanguinetti C, Padua R, Romanini E, Amadio P. Outcome research and patient-oriented measures in the multiperspective assessment of neurological and musculoskeletal disorders. Consensus Conference: Third Roman Neurophysiology Day, Outcome Research in Neurology and in Musculoskeletal Disorders – 24 October 1998. Ital J Neurol Sci. 1999;20(2):139-40. doi:10.1007/s100720050022
10. Raggi A, Leonardi M, Antozzi C, Confalonieri P, Maggi L, Cornelio F et al. Concordance between severity of disease, disability and health-related quality of life in myasthenia gravis. Neurol Sci. 2010;31(1):41-5. doi:10.1007/s10072-009-0167-y
11. Leonardi M, Raggi A, Antozzi C, Confalonieri P, Maggi L, Cornelio F et al. The relationship between health, disability and quality of life in myasthenia gravis: results from an Italian study. J Neurol. 2010;257(1):98-102. doi:10.1007/s00415-009-5279-z
12. Morris J, Perez D, McNoe B. The use of quality of life data in clinical practice. Qual Life Res. 1998;7(1):85-91. doi:10.1023/A:1008893007068
13. Padua L, Evoli A, Aprile I, Caliandro P, Batocchi AP, Punzi C et al. Myasthenia gravis outcome measure: development and validation of a disease-speciic self-administered questionnaire. Neurol Sci. 2002;23(2):59-68. doi:10.1007/s100720200027
14. Wolfe GI, Herbelin L, Nations SP, Foster B, Bryan WW, Barohn RJ. Myasthenia gravis activities of daily living proile. Neurology. 1999;22;52(7):1487. doi:10. 1212/ WNL. 52. 7. 1487
15. Muppidi S. The myasthenia gravis: speciic activities of daily living proile. Ann N Y Acad Sci. 2012;1274(1):114-9. doi:10.1111/j.1749-6632.2012.06817.x
16. Burns TM, Grouse CK, Conaway MR, Sanders DB. Construct and concurrent validation of the MG-QOL15 in the practice setting. Muscle Nerve. 2010;41(2):219-6. doi:10.1002/mus.21609
17. Besinger UA, Toyka KV, Hömberg M, Heininger K, Hohlfeld R, Fateh-Moghadam A. Myasthenia gravis: long-term correlation of binding and bungarotoxin blocking antibodies against
acetylcholine receptors with changes in disease severity. Neurology. 1983;33(10):1316-21. doi:10.1212/WNL.33.10.1316
18. Burns TM, Conaway MR, Cutter GR, Sanders DB Construction of an eficient evaluative instrument for myasthenia gravis: the MG composite. Muscle Nerve. 2008;38(6):1553-62. doi:10.1002/mus.21185
19. Mourão AM, Araújo CM, Barbosa LS, Gomez RS, Burns TM, Lemos SM et al. Brazilian cross-cultural translation and adaptation of the “Questionnaire of Life Quality Speciic for Myasthenia Gravis - 15 items”. Arq. Neuropsiquiatr. 2013;71(12):955-58. doi:10.1590/0004-282X20130180
20. Sadjadi R, Conaway M, Cutter G, Sanders DB, Burns TM. Psychometric evaluation of the myasthenia gravis composite using Rasch analysis. Muscle Nerve. 2012;45(6):820-5. doi:10.1002/mus.23260
21. Guillemin F, Bombardier C, Beaton D. Cross-cultural adaptation of health-related quality of life measures: literature review and proposed guidelines. J Clin Epidemiol. 1993;46(12):1417-32. doi:10.1016/0895-4356(93)90142-N
22. Guillemin F. Cross-cultural adaptation and validation of health status measures. Scand J Rheumatol. 1995;24(2):61-3. doi:10.3109/03009749509099285
23. Reichenheim ME, Moraes CL. Operationalizing the cross-cultural adaptation of epidemological measurement instruments. Rev Saúde Pública. 2007;41(4):665-73. doi:10.1590/S0034-89102006005000035
24. Maher CG, Latimer J, Costa LOP. The relevance of cross-cultural adaptation and clinimetrics for physical therapy instruments. Rev Bras Fisioter. 2007;11(4):245-52. doi:10.1590/S1413-35552007000400002
25. Beaton D, Bombardier C, Guillemin F, Ferraz MB. Guidelines for process of cross-cultural adaptation of self-report measures. Spine. 2000;(25)24:3186-91. doi:10.1097/00007632-200012150-00014
26. Oliveira EF, Urbano JJ, Santos IR, Silva AS, Guimarães LL, Peixoto RAO et al. Brazilian translation, cross-cultural adaptation and validation of the MG Composite scale and Quantitative Myasthenia gravis testing form: a multicentric study protocol. Man Ther Posturology Rehabil J. 2016;14:1-5. doi:10.17784/mtprehabjournal.2016.14.342
27. Benatar M, Sanders DB, Burns TM, Cutter GR, Guptill JT, Baggi F et al. Recommendations for myasthenia gravis clinical trials. Muscle Nerve. 2012;45(6):909-17. doi:10.1002/mus.23330
28. Burns TM, Conaway M, Sanders DB, MG Composite and MG-QOL15
Study Group. The MG Composite. A valid and reliable outcome measure for myasthenia gravis. Neurology. 2010;74(18):1434-40. doi:10.1212/WNL.0b013e3181dc1b1e
29. Burns TM. The MG composite: an outcome measure for myasthenia gravis for use in clinical trials and everyday practice. Ann N Y Acad Sci. 2012;1274(1):99-106. doi:10.1111/j.1749-6632.2012.06812.x
